Integrated vertical trench mos transistor

ABSTRACT

A VTMOS transistor in semiconductor material of a first type of conductivity includes a body region of a second type of conductivity and a source region of the first type of conductivity. A gate region extends into the main surface through the body region and is insulated from the semiconductor material. A region of the gate region extends onto the main surface is insulated from the rest of the gate region. An anode region of the first type of conductivity is formed into said insulated region, and a cathode region of the second type of conductivity is formed into said insulated region in contact with the anode region; the anode region and the cathode region define a thermal diode electrically insulated from the chip.

BACKGROUND

1. Technical Field

The present disclosure generally relates to the field of semiconductor devices. More particularly, the present disclosure relates to vertical gate MOS field effect transistors (or VTMOS, “Vertical Trench-MOS”).

2. Description of the Related Art

A VTMOS transistor integrated on a chip of the semiconductor material comprises a drain region at a rear surface of the chip, a source region at a front surface of the chip opposite the rear surface, and a gate region in a trench extending in the chip from the front surface. More particularly, the walls of the trench are coated with a layer of insulating material (typically, gate oxide), and the trench is filled with a conductive material (typically, polycrystalline silicon or polysilicon).

During operation, a channel region is created along the walls of the trench, between the source region and the drain region. In this way, in the case of a small size of the VTMOS transistor (for example, for making electronic circuits having high integration density), the channel region may be maintained sufficiently long to prevent short channel effects (for example, punch-through or permanently shorted channel) and unwanted changes in characteristic electrical parameters (for example, transconductance).

Although widely used, the VTMOS transistors have drawbacks that preclude a wider deployment thereof, for example, in power applications.

In such applications, the VTMOS transistors, being affected by relatively high voltages and/or currents (for example, 1-500A and 10-100V), are subject to considerable heating; an excessive and/or prolonged heating (or overheating) may cause damages or breakages of the VTMOS transistor even after relatively short periods of use.

In order to avoid that, different solutions are based on the common approach of monitoring the current through the VTMOS transistor, and turn it off when it exceeds a predefined value (associated with an overheating condition). However, such approach involves operation errors, such as false detections of overheating conditions. This is due to the fact that the current monitoring does not allow distinguishing between short-circuit current—which, lasting for typically long times, determines the overheating of the transistor—and switching current—which, limited to a short time interval corresponding to a switching, does not instead determine an appreciable overheating. Furthermore, in the case where the short-circuit current is lower than the predefined value, but lasting for a time sufficiently long to overheat the transistor, the overheating condition is not detected.

A different approach provides for detecting the temperature of the transistor. In a typical implementation, two conductive regions having opposite doping are integrated onto the chip together with the VTMOS transistor to form a corresponding thermal diode; in this way, by exploiting the (inverse) proportionality between the voltage drop across a forward-biased diode and its junction temperature, it is possible to detect the overheating condition in an appropriate manner.

However, the solutions based on such approach are not satisfactory in terms of electrical performance. In fact, as the thermal diode is typically buried within the chip, it affects the current through the VTMOS transistor. In addition, unavoidable couplings between the conductive regions of the diode and the conductive regions of the VTMOS transistor adjacent thereto may determine parasitism (for example, parasitic diodes and/or BJT transistors) able to modify the functioning of the VTMOS transistor and of the thermal diode.

In addition, the presence of the trench reduces the available space on the chip where to make the thermal diode; this makes the establishment of couplings between the conductive regions of the thermal diode and the conductive regions of the VTMOS transistor even more likely (which requires more effort design).

BRIEF SUMMARY

In its general terms, the solution according to one or more embodiments of the present disclosure is based on making the thermal diode in an insulated region of the gate region of the VTMOS transistor.

More specifically, an aspect of the solution according to an embodiment of the present disclosure relates to a method for integrating an electronic device (comprising a VTMOS transistor) onto a chip. A gate structure is formed so as to extend into the chip and onto its main surface; a region of the gate structure that extends on the main surface is insulated from the rest of the gate structure (wherein the gate region is formed), and an anode region and a cathode region in contact with each other are formed into said insulated region to define a thermal diode electrically insulated from the chip.

Another aspect of the solution according to an embodiment of the disclosure relates to an electronic device obtained by such method.

A further aspect of the solution according to an embodiment of the disclosure relates to a system comprising one or more of such electronic devices.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A solution according to one or more embodiments of the disclosure, as well as further features and the advantages thereof, will be best understood with reference to the following detailed description, given purely by way of a non-restrictive indication, to be read in conjunction with the accompanying drawings (wherein, for the sake of ease, corresponding elements are denoted with equal or similar references, and their explanation is not repeated for the sake of brevity). In this respect, it is expressly understood that the figures are not necessarily drawn to scale (with some details that may be exaggerated and/or simplified) and that, unless otherwise indicated, they are simply used to conceptually illustrate the described structures and procedures. In particular:

FIG. 1 schematically shows a sectional view of an electronic device according to an embodiment of the present disclosure;

FIGS. 2A-2F schematically show some significant steps of the production process of such electronic device according to an embodiment of the present disclosure, and

FIG. 3 schematically shows an electronic system according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

With particular reference to FIG. 1, it schematically shows a sectional view of an electronic device 100 (comprising a vertical gate MOS transistor—VTMOS, “Vertical Trench-MOS”—, or transistor 100 _(T), and a thermal diode 100 _(D)) according to an embodiment of the present disclosure.

In the following, the concentrations of N-type and P-type dopants (or impurities) are denoted by adding the sign+ or the sign—to the letters N and P to indicate a high or low concentration of impurities, respectively, or the sign ++ or the sign—to indicate a very high or a very low concentration of impurities, respectively; the letters N and P without the addition of any sign denote intermediate concentrations.

The electronic device 100 is integrated on a chip 105 of semiconductor material of N⁺-type (for example, phosphorus-doped silicon), which has a front surface 105 _(A) and a rear surface 105 _(B) opposite the front surface 105 _(A).

The transistor 100 _(T) comprises a drift region 110 of N⁻-type that extends into the chip 105 from the front surface 105 _(A), a body region 115 of P⁺-type (for example, boron-doped silicon) that extends into the drift region 110 from the front surface 105 _(A), and a source region 120 of N⁺-type that extends into the body region 115 from the front surface 105 _(A)—with such chip 105 that defines, between the drift region 110 and the rear surface 105 _(B), a corresponding drain region 125.

The transistor 100 _(T) further comprises a gate region 130 of conductive material (for example, polysilicon with N⁺-type doping), which extends vertically into the drift region 110 from the front surface 105 _(A) (through the body region 115 and the source region 120) and it is electrically insulated from the chip 105 (by means of an insulating layer 135).

As visible in the figure, the gate region 130 protrudes in height beyond the front surface 105 _(A), and extends also onto at least part of it. Furthermore, a region 130 _(INS) separated from the gate region 130 and insulated from the chip 105 (through the same insulating layer 135) is provided on the front surface 105 _(A), inside which an N⁺-type conductive region and a P⁺-type conductive region in contact with each other define an anode region A and a cathode region K, respectively, of the thermal diode 100 _(D).

Compared to the known solutions, where the thermal diode is electrically connected to the chip, in the solution according to an embodiment of the present disclosure the thermal diode 100 _(D) is integrated on the chip 105 but completely insulated from it (i.e., floating). In this way, the thermal diode 100 _(D) may be used to adequately detect overheating conditions of the transistor 100 _(T), without inducing parasitism within the chip 105 and without affecting the current through the transistor 100 _(T).

The electronic device 100 further comprises a dielectric region 140, which extends on the cathode region K, the anode region A, the gate region 130 and exposed portions of the dielectric layer 135 to provide electrical insulation and mechanical protection to the chip 105, and terminals for accessing the conductive regions.

More particularly, the electronic device 100 comprises a source terminal T_(S), a gate terminal T_(G), a cathode terminal T_(K) and an anode terminal T_(A) exposed on a top surface of the dielectric region 140, and a drain terminal T_(D) on the rear surface 105 _(B) of the chip 105. The terminals T_(S),T_(G),T_(K),T_(A) are connected, by means of corresponding via-holes through the dielectric region 140, to the source region 120, the gate region 130, the cathode region K and the anode region A, respectively (with the terminal T_(S) in a rearward position with respect to the terminal T_(G)—as conceptually represented in the figure by dotted lines of the corresponding via-hole—so as not to contact the gate region 130), whereas the terminal T_(D) is directly connected to the drain region 125.

Turning to FIGS. 2A-2F, they schematically show some significant steps of the production process of the electronic device 100 according to an embodiment of the present disclosure.

As it is known, the production process is performed at the level of a batch of completely identical electronic devices 100, which are concurrently made in large numbers onto a wafer of semiconductor material and separated at the end through a cutting operation (for the sake of description ease, however, reference to only one of such electronic devices will be made in the following).

Considering in particular FIG. 2A, the production process starts with the making of a trench 205 (for example, having a U-shaped section) extending into the chip 105 from the front surface 105 _(A). As visible in the figure, at this stage the chip 105 has mainly a N⁻-type doping (for example, obtained in a known manner before the making of the trench 205) and it only comprises the drain region 125 (however, in an alternative embodiment discussed below, at this stage the chip 105 may also comprise the drift region 110, the body region 115 and/or the source region 120).

Turning now to FIG. 2B, the insulating layer 135 (e.g., silicon oxide) is formed onto the front surface 105 _(A) and onto a boundary surface of the trench 205 (i.e., onto—side and end—exposed walls thereof), a conductive layer 210 (for example, of un-doped polysilicon) is deposited onto the insulating layer 135, and a further conductive layer 215 (for example, of N⁺-doped polysilicon) is deposited onto the conductive layer 210 (so as to fill the trench 205). The layers 135, 210, 215 do not completely cover the front surface 105 _(A) (as exposed portions of the front surface 105 _(A) are used for other purposes, for example, for subsequent contact of the source region); therefore such layers 135, 210, 215 are formed by selective processes, or by non-selective processes followed by selective etching.

As shown in FIG. 2C, the workpiece thereby obtained is subject to a surface planarization treatment (for example, a chemical-mechanical polishing) for removing the conductive layer 215 outside the trench 205. In this way a gate structure 230 is obtained that comprises the insulating layer 135, exposed portions of the conductive layer 210 on the front surface 105 _(A), and portions of the conductive layers 210, 215 within the trench 205—as will be explained shortly, both the thermal diode and the gate region of the transistor will be made from such gate structure 230.

Then, a photo-resist mask, not shown in the figure, is formed onto the gate structure 230 by means of a photo-lithographic technique; portions of the gate structure 230 being not protected by the mask are etched—for example, through a dry etching operation. The result of such operation is shown in FIG. 2D, with the making of the insulated region 130 _(INS) and of a conductive region 230 _(D) (that will form the gate region 130)—anyway, although advantageous in terms of construction symmetry, the making of the conductive region 230 _(D) may be omitted, in which case the gate region 130 may be defined from the gate structure 230 without the insulated region 130 _(INS).

At this point, as shown in FIG. 2E, a single ion implantation process of N⁺⁻type dopant is carried out into a part of the insulated region 130 _(INS) so as to define the anode region A, into the rest of the gate structure (i.e., in the conductive region 230 _(D) in the example at issue) so as to define the gate region 130 (with uniform doping), and into the chip 105 so as to define the source region 120. This is achieved by defining (by means of suitable masks, not shown) the implantation areas, and performing an ion bombardment with controlled dopant diffusion (for example, by controlling implantation energies and time). It should be noted that, although not visible in the figure (because of the used viewpoint), the source region 120 will be provided with N⁻-doped zones (instead of N⁺ ones) at (i.e., below) the regions A,K and at portions of the gate region 130 laterally protruding from the trench—because of the “masking” induced by them. Anyway, such N⁻-doped zones, having negligible size (compared to the source region 120), do not involve changes of the electrical characteristics of the electronic device 100.

Then, as shown in FIG. 2F, a single process of ion implantation of P⁺-type dopant (analogous to the previous one) is carried out into another part of the insulated region 130 _(INS) so as to define the cathode region K, and into the chip 105 so as to define the body region 115 (and hence the drift region 110 interposed between it and the drain region 125). As before, the body region 115 will be provided with N⁺-doped zones (instead of P⁺ ones) below the regions A, K and the portions of the gate region 130 laterally protruding from the trench. In any case, similarly to what has been discussed above, such N⁺-doped zones, having negligible size (compared to the body region 115), do not involve changes of the electrical characteristics of the electronic device 100.

At this point, the production process ends, in a known manner, with the deposition of the dielectric region 140 and with the making of the terminals T_(S),T_(G),T_(K),T_(A),T_(D), as shown in FIG. 1.

The described solution is advantageous as it allows making the thermal diode 100 _(D) contextually to the source region 120, the body region 115 and the gate region 130; this allows obtaining a simple and efficient production process, which does not require additional mask levels nor dedicated diffusion or implantation layers (with corresponding cost reduction).

With reference now to FIG. 3, it schematically shows an electronic system 300 according to an embodiment of the present disclosure.

The electronic system 300 comprises the electronic device 100 (or more of them), shown in the figure by circuit representation of the transistor 100 _(T) and of the corresponding thermal diode 100 _(D) electrically insulated from it.

The electronic system 300 further comprises a biasing element 305 (e.g., a bias current generator, indicated in the figure by means of its circuit symbol), connected between the terminals T_(K) and T_(A) to provide a bias current to the thermal diode 100, and a measuring circuit 310, also connected between the terminals T_(K) and T_(A), for measuring a voltage across the thermal diode 100 _(D).

The electronic system 300 further comprises a processing circuit 315 for determining an operating temperature of the transistor 100 _(T) according to the corresponding measured voltage (according to the inverse proportionality relationship between the voltage across a forward-biased diode and its junction temperature—in the specific case, in turn determined by the operating temperature of the transistor 100 _(T)). In the described embodiment, the processing circuit 315 is also connected to the gate terminal T_(G) for controlling the operation of the transistor 100 _(T) according to the determined operating temperature.

Such solution is advantageous as, through the thermal diode 100, it is possible to determine the operating temperature of the transistor 100 _(T) without affecting the current through it.

Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many logical and/or physical modifications and alterations. More specifically, although this solution has been described with a certain degree of particularity with reference to one or more embodiments thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible. Particularly, different embodiments of the disclosure may even be practiced without the specific details (such as the numerical examples) set forth in the preceding description to provide a more thorough understanding thereof; conversely, well-known features may have been omitted or simplified in order not to obscure the description with unnecessary particulars. Moreover, it is expressly intended that specific elements and/or method steps described in connection with any embodiment of the disclosed solution may be incorporated in any other embodiment as a matter of general design choice. In any case, ordinal qualifiers or the like are merely used as labels for distinguishing elements with the same name but do not connote any priority, precedence or order. Moreover, the terms including, comprising, having and containing (and any of their forms) should be understood with an open and non-exhaustive meaning (i.e., not limited to the recited elements), the terms based on, dependent on, according to, function of (and any of their forms) should be understood as a non-exclusive relationship (i.e., with possible further variables involved) and the term a should be understood as one or more elements (unless expressly stated otherwise).

For example, an embodiment of the present disclosure proposes a method for integrating an electronic device comprising a VTMOS transistor onto a chip of semiconductor material of a first type of conductivity. The method comprises the following steps. A body region of a second type of conductivity extending into the chip from a main surface of the chip is formed. A source region of the first type of conductivity extending into the body region from the main surface is formed. A gate region of conductive material extending into the chip from the main surface is formed through the body region; the gate region is insulated from the chip. In the solution according to one or more embodiments of the present disclosure, the step of forming a gate region comprises forming a gate structure extending into the chip from the main surface through the body region and onto the main surface. The method further comprises the following steps. A region of the gate structure extending on the main surface is insulated from the rest of the gate structure; the gate region is obtained from said rest of the gate structure. An anode region of the first type of conductivity is formed into said insulated region, and a cathode region of the second type of conductivity is formed into said insulated region in contact with the anode region; the anode region and the cathode region define a thermal diode electrically insulated from the chip.

Anyway, although in the present description explicit reference has been made to a chip integrating a single VTMOS transistor and a single thermal diode, this should not to be understood in a limitative way. In general, number and type of electronic components integrated onto the chip may be any; for example, it is possible to envisage the use of a greater number of thermal diodes associated with the same transistor (in which case, it may be necessary to form a higher number of insulated regions in the same chip). Furthermore, similar considerations apply if the N-type regions are replaced by P-type regions, and vice-versa, or if the various regions have different impurities concentrations(for example, N⁺⁺, P⁻⁺ or N⁻, P⁻ dopings); moreover, the conductive regions of the transistor may have any shape, size, position and number.

According to an embodiment of the present disclosure, the step of forming a gate structure comprises the following steps. A trench extending into the chip from the main surface is formed through the body region. An insulating layer is formed onto the main surface and onto a boundary surface of the trench. A first conductive layer is formed onto the insulating layer. A second conductive layer is formed onto the first conductive layer so as to fill the trench. The second conductive layer is removed outside the trench so as to expose the first conductive layer on the main surface thereby defining the gate structure.

Although in the description reference has been made to a “U”-shaped trench, this does not prevent from making it with any other suitable shape. In addition, the trench may extend into the chip without reaching the drift region (for example, by extending not beyond the body region). The insulating layer may comprise, as previously described, silicon oxide—so that it may be formed by a known growth process. Alternatively, the insulating layer may comprise any other material with appropriate dielectric properties obtained by any suitable deposition technique (for example, chemical vapor deposition). Moreover, the making of the gate structure by a single layer of conductive material is not excluded.

According to an embodiment of the present disclosure, the first conductive layer comprises un-doped polysilicon, and the second conductive layer comprises doped polysilicon.

Anyway, the first conductive layer and the second conductive layer may comprise any material. For example, they may be both of un-doped polysilicon (in this way, the following dopant implantation would allow obtaining a gate region with highly uniform doping).

According to an embodiment of the present disclosure, the step of removing the second conductive layer outside the trench comprises performing a chemical-mechanical polishing.

Anyway, such step may also be omitted in a basic implementation (for example, in case of controlled deposition of the second conductive layer only into the trench), or it may be implemented by any other ablation technique.

According to an embodiment of the present disclosure, the step of insulating a region of the gate structure comprises removing a portion of the first conductive layer.

Anyway, such step may be omitted as well (for example, in case of implementation of the insulation by means of interposition of an insulating structure, or in case the insulated region is formed—for example, thanks to the use of selective techniques—already separated from the rest of the gate structure).

According to an embodiment of the present disclosure, the step of forming an anode region comprises performing a first ion implantation of dopant of the first type of conductivity into a first part of the first conductive layer defining said insulated region, and the step of forming a cathode region comprises performing a second ion implantation of dopant of the second type of conductivity into a second part of the first conductive layer defining said insulated region.

Such ion implantations may be made in succession (as exemplarily described above), or in any other order.

According to an embodiment of the present disclosure, the step of forming a gate region comprises performing said first ion implantation of dopant of the first type of conductivity further into at least part of the rest of the gate structure, and the step of forming a body region comprises performing said second ion implantation of dopant of the second type of conductivity further into the chip.

As before, such ion implantations may be performed in succession (as exemplarily described above), or in any other order. Furthermore, the ion implantation of dopant for obtaining the gate region may be performed onto all the rest of the gate structure (for example, for obtaining a gate region that extends laterally far beyond the trench). Anyway, the making of the source region and/or of the body region independently of the making of the thermal diode is not excluded; in this respect, in an alternative embodiment, not shown, the starting structure for implementing the described solution may comprise the chip with the drain region, the drift region, the body region and the source region being already formed.

In general, the solution according to an embodiment of the disclosure lends itself to be implemented through an equivalent method (by using similar steps, removing some non-essential steps, or adding additional optional steps); moreover, the steps may be performed in a different order, in parallel or overlapped (at least in part).

An embodiment of the present disclosure proposes an electronic device comprising a VTMOS transistor integrated on a chip of semiconductor material of a first type of conductivity. The electronic device comprises a body region of a second type of conductivity extending in the chip from a main surface of the chip, a source region of the first type of conductivity extending in the body region from the main surface, and a gate region of conductive material extending in the chip from the main surface through the body region; the gate region is insulated from the chip. In the solution according to one or more embodiments of the present disclosure, the electronic device comprises a region insulated from the gate region and from the chip on the main surface of the chip, an anode region of the first type of conductivity in said insulated region, and a cathode region of the second type of conductivity in said insulated region in contact with the anode region. The anode region and the cathode region define a thermal diode electrically insulated from the chip.

Anyway, similar considerations apply if the electronic device has a different structure or comprises equivalent components. In any case, any of its components may be separated into several elements, or two or more components may be combined into a single element; in addition, each component may be replicated to support the execution of the corresponding operations in parallel. It should also be noted that (unless stated otherwise) any interaction between different components generally does not need be continuous, and it may be direct or indirect via one or more intermediaries.

For example, the number of via-holes is not limitative, and it does not necessarily coincide with the number of terminals of the chip. Furthermore, the number of terminals is not limitative. Each terminal may have one or more pads, and each pad may be associated with multiple via-holes. In addition, the size and distribution of the terminals may be chosen according to electrical and mechanical considerations. In this respect, the source terminal may be formed next to the gate terminal (for example, after removal of a part of the conductive layer above the source region).

It should be understood that the design of the electronic device may also be created in a programming language; in addition, if the designer does not manufacture the corresponding integrated devices or masks, the design may be transmitted by physical means to others. In any case, the resulting integrated circuit may be distributed by its manufacturer in raw wafer form, as a bare die, or in packages. Moreover, the proposed structure may be integrated with other circuits on the same chip, or it may be mounted in intermediate products (such as mother boards) and coupled with one or more other chips (such as a processor).

An embodiment of the present disclosure proposes a system comprising at least one electronic device. The system further comprises means for biasing the thermal diode of each electronic device, means for measuring an electrical quantity of the thermal diode of each electronic device, and means for determining an operating temperature of each VTMOS transistor according to the corresponding measured electrical quantity.

However, the electronic device may be used in any other application, and may obviously be made and marketed as a stand-alone product as well.

The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A method, comprising: forming an electronic device having a vertical trench MOS transistor in a semiconductor material of a first type of conductivity, the forming of the electronic device includes: forming a body region of a second type of conductivity extending into the semiconductor material from a main surface of the semiconductor material; forming a source region of the first type of conductivity extending into the body region from the main surface; forming a gate region of conductive material extending into the semiconductor material from the main surface through the body region, the gate region being insulated from the semiconductor material, the forming of the gate region including: forming a gate structure extending into the semiconductor material from the main surface through the body region and onto the main surface; insulating a region of the gate structure extending on the main surface from a remainder of the gate structure; and forming the gate region from the remainder of the gate structure; forming an anode region of the first type of conductivity into said insulated region; and forming a cathode region of the second type of conductivity into said insulated region in contact with the anode region, the anode region and the cathode region defining a thermal diode electrically insulated from the semiconductor material.
 2. The method according to claim 1 wherein forming the gate structure comprises: forming a trench extending into the semiconductor material from the main surface through the body region; forming an insulating layer onto the main surface and onto a boundary surface of the trench; forming a first conductive layer onto the insulating layer; forming a second conductive layer onto the first conductive layer to fill the trench; and removing the second conductive layer outside the trench to expose the first conductive layer on the main surface.
 3. The method according to claim 2 wherein the first conductive layer includes un-doped polysilicon, and the second conductive layer includes doped polysilicon.
 4. The method according to claim 2 wherein the removing the second conductive layer outside the trench includes: performing a chemical-mechanical polishing.
 5. The method according to claim 2 wherein the insulating a region of the gate structure includes: removing a portion of the first conductive layer.
 6. The method according to claim 2 wherein the forming an anode region includes: performing a first ion implantation of dopants of the first type of conductivity into a first part of the first conductive layer defining said insulated region; and wherein the forming a cathode region includes: performing a second ion implantation of dopants of the second type of conductivity into a second part of the first conductive layer defining said insulated region.
 7. The method according to claim 6 wherein the forming a gate region includes: performing said first ion implantation of dopants of the first type of conductivity further into at least part of the remainder of the gate structure; and wherein the forming a body region includes: performing said second ion implantation of dopants of the second type of conductivity further into the semiconductor material.
 8. An electronic device, comprising: a semiconductor substrate of a first type of conductivity; a vertical trench MOS transistor integrated in the semiconductor substrate; a body region of a second type of conductivity extending in the semiconductor substrate from a main surface of the semiconductor substrate; a source region of the first type of conductivity extending in the body region from the main surface; a gate region of conductive material extending in the semiconductor substrate from the main surface through the body region, the gate region being insulated from the semiconductor substrate; a region insulated from the gate region and from the semiconductor substrate on the main surface; a thermal diode electrically insulated from the semiconductor substrate, the thermal diode including: an anode region of the first type of conductivity in said insulated region; and a cathode region of the second type of conductivity in said insulated region in contact with the anode region, the anode region and the cathode region.
 9. The device of claim 8 wherein the gate structure includes: a trench extending into the semiconductor substrate from the main surface through the body region; an insulating layer onto the main surface and onto a boundary surface of the trench; a first conductive layer onto the insulating layer; and a second conductive layer onto the first conductive layer to fill the trench.
 10. A system, comprising: an electronic device that includes: a semiconductor substrate of a first type of conductivity; a vertical trench MOS transistor integrated on the semiconductor substrate; a body region of a second type of conductivity extending in the semiconductor substrate from a main surface of the semiconductor substrate; a source region of the first type of conductivity extending in the body region from the main surface; a gate region of conductive material extending in the semiconductor substrate from the main surface through the body region, the gate region being insulated from the semiconductor substrate; a region insulated from the gate region and from the semiconductor substrate on the main surface; a thermal diode electrically insulated from the semiconductor substrate, the thermal diode including: an anode region of the first type of conductivity in said insulated region; and a cathode region of the second type of conductivity in said insulated region in contact with the anode region, the anode region and the cathode region; and a first module configured to bias the thermal diode; a second module configured to measure an electrical quantity of the thermal diode; and a third module configured to determine an operating temperature of each vertical trench MOS transistor in response to the measured electrical quantity.
 11. The system of claim 10 wherein the gate structure includes: a trench extending into the semiconductor substrate from the main surface through the body region; an insulating layer onto the main surface and onto a boundary surface of the trench; a first conductive layer onto the insulating layer; and a second conductive layer onto the first conductive layer to fill the trench.
 12. A device, comprising: a substrate having a first surface and a second surface; a transistor formed in the substrate, the transistor including: a first terminal formed on the second surface of the substrate; a second terminal formed on the first surface of the substrate; a gate formed on and in the substrate; an insulating layer configured to separate the gate from the substrate; a thermal diode formed on the substrate and being thermally isolated from the substrate by the insulating layer, the thermal diode including: an anode spaced from the gate by a distance; and a cathode separated from the gate by the anode.
 13. The device of claim 12 wherein the substrate includes a layer of a first conductivity type adjacent to the first terminal and a body region of a second conductivity type.
 14. The device of claim 12, further comprising a trench, the gate being formed in the trench.
 15. The device of claim 14 wherein the insulating layer is on the second surface of the substrate and on an interior surface of the trench.
 16. The device of claim 15 wherein the gate includes a first portion in the trench and second portions that are above the first surface of the substrate and extend further than the interior surface of the trench. 